Table IV. initiating or cancer-promoting agents and cocarcinogenic compounds in smoke from residential wood combustion sources.(a,b)

a DeAngelis, et al.(21) (grams emissions per kilogram wood)
b Van Duuren(32)

This is of concern because these conditions are relatively common in the winter when emissions from this source would be highest. Not only would this source contribute significantly to the general air pollution levels during these acute episodes, but their emissions are highly respirable and contain potentially hazardous materials as noted in Tables I-IV. In addition, this material is emitted in residential areas where the very young and old portion of the population, as well as those with special medical problems, will receive the maximum exposure. These emissions may also be difficult to turn off during periods of acute air pollution episodes in the winter, if a significant portion of the population depends on RWC as their primary energy source.

England has already recognized the contribution of this source to its air pollution episodes and has banned the use of soft coal and wood for heating in London and other smoke control areas in England.39 ln addition, most metropolitan areas of the U.S. have banned backyard trash incineration and simply moving the incinerator indoors doesn't make the emissions any more environmentally acceptable. The trend towards increasing solid waste disposal costs will continue to encourage the use of RWC devices as incinerators of kitchen trash which along with soot cleaners will greatly complicate the chemistry of the emissions.

Chronic health effects related to most forms of air pollution are much more difficult to assess. The effects are often sub clinical and difficult to distinguish from other effects such as ' infectious diseases, cigarette smoking, and personal habits in addition to having potentially long latent periods. Nevertheless, enough information is available to show clearly that the emissions from RWC appliances are a potential threat to public health relative to many other sources of air pollutants.

There are numerous clinical and sub clinical respiratory and nonrespiratory health effects to which RWC emissions could contribute by simply increasing the level or general air pollution. These include not only cancer, but also chronic and acute bronchitis, the common cold, pneumonia, emphysema, asthma, etc.(40) The hazardous chemicals emitted from RWC sources and their highly respirable nature, however, must raise an additional level of concern for this source of air pollution beyond its contribution to general air pollution levels. This concern is based in part on the following information:

• Cancer of the skin in chimney sweeps was associated with soot as early as 1775.(41) Since then, soots from a variety of fuels including wood have been shown to be carcinogenic.(29,42) The major carcinogenic compounds identified in soot have been found in wood smoke.(21,31,42) The carcinogenicity of benzo(a)pyrene, a strong cancer causing agent found in soot, is increased in the presence of carbon particulates and S02.(43,44)
• Cigarette smoke is known to cause cancer in humans. The combustion of carbonaceous materials in general, is known to produce similar chemical compounds. Some of the same strong cancer causing 'chemicals found in cigarette smoke have also been found to be abundant in wood smoke.(21,44) More than 2000 compounds have been identified in cigarette smoke.(45,46) Although only about 100 have been identified so far in wood smoke, it is reasonable to assume that many more of the same compounds found in cigarette smoke will be found in wood smoke.
• Villagers in the Highlands of New Guinea, who are constantly exposed to high levels of smoke from tires in small enclosed huts, develop obstructive lung diseases by the time they are 40 years old.(47)
• High levels of industrial exposure to strong carcinogens as indicated by benzo(a)pyrene found in wood smoke have been shown to elevate the risk of lung cancer.(48,49)
• Soot associated with industrial processes is considered by EPA to be associated with cancer induction in human lungs and skin on the basis of epidemiological evi· dence.(50)
• "It appears both reasonable and prudent to take as a working hypothesis the existence of a causal relation between air pollution and lung cancer death rate at the rate of a 5% increase for each increment of pollution as indexed by 1 benzo[¤]pyrene unit."-Committee on Biological Effects of Atmospheric Pollutants, National Research Council.(51)
• A large number of carcinogens including benzo(a)pyrene have been shown to be abundantly present in wood smoke.(21)
• Cilia toxic, mucus coagulating, co-carcinogenic, priority pollutants, toxic, noxious and irritating chemicals are present.(21)

Thus, emissions from RWC sources must be considered a potential major threat to public health because of their highly respirable nature, the hazardous chemicals they contain, the available information relating these emissions, chemicals, etc. to health related problems, the fact that they are emitted in residential areas, and that the emissions are increasing.

The extent of exposure to these pollutants must be known before the environmental and health impact of this source of air pollution can be fully assessed. This will require more than simple emission inventories. Methods must be developed and applied which will allow the direct quantitative determination of the levels of wood smoke pollutants in several regions of the country over extended periods of time and both inside and outside of residences. In the meantime, emphasis needs to be placed on further evaluation of the health risks of the priority and carcinogenic pollutants in smoke. This would provide some of the basic information required to assess the absolute health risks as well as the health risks relative to other major sources of pollution such as transportation and industrial point sources.

Table V. National Ambient Air Quality Standards.This table is omitted because this paper was written in 1980 and the standards have changed.

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